The invention relates to an intake system for an internal combustion engine having a cylinder head with an inlet duct including a control flap, which is pivotally supported for controlling the gas flow through the inlet duct.
U.S. Pat. No. 5,477,823 discloses an intake system for an internal combustion engine that has a cylinder head with one inlet duct per cylinder, which branches downstream into component ducts leading to different inlet valves. A flange part with a control flap for the purpose of generating turbulence in the inlet duct is supported upstream of the cylinder head mounting flange. The control flap is supported on a roller rotatably mounted slightly eccentrically in the flange part. In an opened position, the flap closes a dead volume in the flange part in such a way that the flap is flush with the duct wall. In the closed position, the control flap projects partially into the dead volume and partially into the inlet duct in order to generate there a turbulent flow that leads to a tumbling flow in the combustion chamber of the associated cylinder.
It is the object of the invention to provide a control flap with improved flow properties while reducing the expenses and space requirements for the design.
In an intake system for an internal combustion engine having a cylinder head with at least one inlet duct per cylinder, an essentially flat control flap is supported in the inlet duct on a pivot shaft pivotally about an axis which is disposed in spaced relationship upstream from the control flap by way of side support arms such that, in an open position, the control flap rests against a wall portion of the inlet duct from where it can be swiveled out into the intake duct into a flow directing, turbulence generating position.
When the control flap is not intended to generate turbulence, it is located in such a way that it hinders the flow in the inlet duct as little as possible. In a turbulence-generating position, which is set in certain ranges of the engine performance graph in order to generate a non-uniform flow profile over the cross-section of the inlet duct, the control flap is pivoted into the flow of the inlet duct. A non-uniform flow profile over the cross-section of the inlet duct causes what is referred to as tumbling flow in the combustion chamber, which results in advantages during combustion with respect to exhaust gas emissions and fuel consumption. A tumbling flow has a cylindrical flow pattern in the combustion chamber about an axis perpendicular to the axis of the cylinder. The pivot axis of the control flap which lies outside the surface of the control flap, is preferably arranged upstream of the control flap because this allows a relatively small actuating force and simple stabilization of the control flap in the flow by virtue of the air flow forces effective on the control flap.
It is advantageous if the control flap has no pivot shaft in the region of the flow. This can be achieved if the pivot shaft is disposed and supported only in the wall of intake duct or the flange part thereof. Within the intake duct, only side portions of the flap, that is support arms, extend to the ends of pivot shaft sections projecting from the wall at each side of the control flap. The side portions or support arms are shaped in such a way that they rest smoothly against the wall of the inlet duct when the control flap is closed. Impairment of the flow in the intake pipe due to the pivot shaft is thereby avoided.
As a refinement of the invention, the control flap is designed in such a way that it rests snugly against a wall of the inlet duct when it is in an open position. This reduces impairment of the flow in the inlet duct when the control flap is in the open position.
Preferably, the control flap rests in a niche in the wall of the inlet duct in its fully open position. As a result, the maximum possible flow cross of the intake duct is provided in the open position of the control flap and the flow in the inlet duct is not impaired.
In a further refinement of the invention, the control flap and the wall or niche for receiving the opened control flap are shaped in such a way that there is only a very small gap between the niche and the control flap in an open position of the control flap. This has the advantage that only a small flap volume in the wall or niche has to be filled or emptied during the actuation of the control flap. If the flap volume is only very small due to the small space, only a very small quantity of fuel or particles from recirculated exhaust gas can collect in the gap. Careful ventilation of the air gap ensures that deposits of whatever kind, that could accumulate in the space when the flap is open, are swept away by the air flow through the space and that clogging of the space by baked-on or boiled-on deposits is avoided.
In a further refinement of the invention, the pivot shaft of the control flap is arranged in such a way that it does not intersect a normal, that is, a line perpendicular to the centroid of the control flap. Since the resultant pressure force of the inlet duct flow acts on the centroid, self-amplification of the movement of the flap into a position for turbulence or in the direction of an opened position is possible in a simple way by moving the pivot axis of the control flap away from a line extending through the centroid and normal to the plane of the control flap. In this case, the actuating force required to move the control flap in a turbulence-generating direction is reduced, that is, a self-amplification is achieved.
On the other hand, the actuating force required to move the flap into the open position is increased over the force required with the pivot axis extending through the normal line on the centroid.
In still a further refinement of the invention, the pivot axis of the control flap lies outside the center of the inlet duct. Eccentric arrangement of the pivot axis makes it possible to provide any lever length between the control flap and the pivot axis, that is, different force ratios between the adjusting force at the pivot axis and the force resulting from the pressure of the flow on the control flap can be established.
In a particular embodiment of the invention, the pivot shaft of the control flap is disposed close to the duct wall of the inlet duct, more specifically on the side that lies opposite the niche for receiving the opened control flap. This arrangement of the pivot results in a long lever arm between the pivot axis and the control flap. Furthermore, the pivot shaft, together with the control flap, can be mounted in the flange part from the outside in an insert without the need for the pivot shaft to extend through the inlet duct in the flange part.
Preferably, the control flap is aerodynamically shaped. This means that the flap has a certain flow profile in order to achieve flow control without completely closing the inlet duct at one side. The flow profile is such that the flow in the inlet duct is directed toward one side of the inlet duct and generates a tumbling flow in the combustion chamber of the internal combustion engine. At the same time, an aerodynamic configuration of the control flap has a lower resistance and hence results in a smaller throttling loss for the air flow. By virtue of the aerodynamic configuration, the control flap can be made smaller while achieving the same effect.
Further features and combinations of features will become apparent from the description and the drawings. Concrete exemplary embodiments of the invention are illustrated in simplified form in the drawings and explained in greater detail in the following description.